The present invention relates to a catalyzer installation for spark-ignition engines which are, in particular, run "rich", i.e. sub-stoichiometric at an air/fuel ratio less than 1.
The use of the known 3-way catalyzers is conditional on the presence of an injection system, or electrically controlled carburetor, because only these permit operation of the spark-ignition engine in the so-called "lambda window", i.e. at between .lambda.=0.98 and .lambda.=1.02 for the required high levels of pollutant reduction. Uncontrolled catalyzers require that the mixture be kept between .lambda.=0.95 and .lambda.=1.03 over the whole of the operating characteristics; they only, however, provide pollutant reductions of, on average, 50%.